One of the most important applications of graphite is as electrodes for arc melting of steel. During the past 20 years the use of electric furnaces for melting steel has grown from a small volume specialty process to a high volume process with probably the lowest production costs of any of the recognized metallurgical processes. The process typically consumes from 10-12 pounds of graphite electrode for each ton of steel produced, or about 8% of the total production cost.
During operation of electric arc steel furnaces, the graphite electrodes are subject to mechanical, chemical and electrical stresses of such severity, that particularly for ultra high powered furnaces, only graphite of very high quality can be used. The electrodes are subject to the mechanical stresses from falling scrap being melted, from the inductance caused by the high AC current and also subject to oxidation due to the temperature reached, which will range up to the graphite sublimation temperature of over 3000.degree. C.
Although pure graphite is one of the most inert and least reactive materials known, oxidation is a highly significant cause of deterioration of strength and loss of material at these extremely high temperatures encountered in an electric arc furnace. Thus, retardation of the oxidation reactions could be highly beneficial in reducing electrode consumption, both by reduction of direct oxidation and by lessening breakage caused by oxidation-induced loss of electrode strength.
During operation of an electric arc furnace, normally three electrodes are used, each of which is connected to one phase of the power supply through a metal clamp, and as the electrode is consumed, additional sections are added at the top and the column lowered to the operating level in the furnace. Although it is generally found that oxidation retardants are ineffective above about 1200.degree. C., any improvement, even at lower temperatures, is welcome and can significantly reduce electrode consumption.
Oxidation retardant solutions have been used by graphite manufacturers to treat electrode sockets for many years. There have also been many attempts to use these solutions as oxidation retardants on the graphite electrodes themselves. However, these have been unsuccessful in the past due to a variety of shortcomings of such treatments including poor oxidation retardation on the electrodes, increased corrosion of the electrode holder, and arcing between the electrode and the electrode holder caused by the presence of a non-conductive film between the electrode and its holder. This non-conductive film which forms between the electrode and its holder or on the holder itself is caused by the prior-art oxidation retardant electrode treating solutions, especially phosphate-containing treating solutions, which cause a non-conductive film of copper phosphate to deposit upon copper electrode holders or at the electrode/electrode holder interface.
The build up of such a non-conductive film causes premature deterioration of the copper electrode holders. A solution to this problem of a non-conductive film build up would be desirable since it would increase the life of costly copper electrode holders, providing a valuable economic savings.